High capacity electrochemically active materials are very desirable for battery applications. However, these materials exhibit substantial volume changes during battery cycling, e.g., swelling during lithiation and contracting during delithiation. For example, silicon swells as much as 400% during lithiation to its theoretical capacity of about 4200 mAh/g or Li4.4Si structure. Volume changes of this magnitude cause pulverization of active materials structures, losses of electrical connections, and capacity fading.
Providing high capacity materials as nanostructures can address some of these issues. Nanostructures have at least one nanoscale dimension, and swelling-contracting along this dimension tends to be less destructive than along larger sides and dimensions. As such, nanostructures can remain substantially intact during battery cycling. However, integrating multiple nanostructures into battery electrode layers that have adequate active material loadings is difficult. Such integration involves establishing and maintaining electrical interconnections between such nanostructures and current collectors and providing mechanical support to these nanostructures on the current collectors or some other substrates over many cycles. Further, smaller nanostructures often do not provide adequate amounts of high capacity active materials in certain electrode designs. For example, depositing a nanofilm onto a conventional flat substrate does not provide adequate active material loading if the nanofilm is kept thinner than typical fracture limits of high capacity active materials. Furthermore, many processes proposed for fabricating nanostructures are slow and often involve expensive materials. For example, etching silicon nanowires from bulk particles uses silver catalysts and expensive etching solution. Growing long crystalline silicon structures can also be a relative slow process and may involve expensive catalysts, such as gold.